The present invention relates generally to magnetron devices, and more particularly, to a solid state magnetron switcher employing insulated gate bipolar junction transistors for switching high voltage pulses among multiple magnetrons.
The prior art approach to switching high voltage pulses among multiple magnetrons is disclosed in U.S. patent application Ser. No. 08/652,889, filed May 23, 1996, entitled xe2x80x9cThyratron Switched Beam Steering Arrayxe2x80x9d, assigned to the assignee of the present invention. The approach disclosed in this patent application provides for a reasonably fast switching scheme with relatively small compactness. However, this approach cannot be directly commanded OFF and relies on a power supply pulse to be discontinued. This approach requires and generates hundreds of watts of heat. It was found that noise emissions using this approach were relatively high and the effects were difficult to deal with.
Prior art switching devices such as those disclosed in the above-cited patent application, have utilized thyratrons as switches instead of IGBT devices. Thyratrons require extensive filament and reservoir power which produces high temperature heat loads. Thyratrons emit a large amount of plasma noise when switched which can adversely affect operation of the magnetrons. Also, these devices cannot be commanded Off and must rely on the power supply high voltage pulse to be discontinued.
Therefore, it would be an advantage to rapidly switch several microwave tubes On and Off while driven from a single high voltage power supply. Accordingly, it is an objective of the present invention to provide for an improved solid state magnetron switcher for switching high voltage pulses among multiple magnetrons.
To accomplish the above and other objectives, the present invention provides for a solid state magnetron switcher that switches high voltage pulses among multiple magnetrons. The present invention switches high voltage to multiple magnetrons thereby gating them ON and OFF. The present invention provides for a small, light-weight, efficient, and fast switching mechanism that offers both ON and OFF control.
More particularly, the solid state magnetron switcher comprises a plurality of magnetrons, one insulated gate bipolar junction transistor (IGBT) high voltage switch coupled to each magnetron, a trigger circuit coupled to each IGBT high voltage switch, an isolation transformer coupled to the trigger circuit, and a floating resistor coupled across each of the IGBT high voltage switches.
The present invention provides a versatile solution to drive multiple magnetrons with a single high voltage pulse power supply. For a system requiring the use of an incoherent RF source, such as a magnetron, this solution is ideal for meeting the stringent objectives of rapidly switching a microwave tube on and off several times a second with long millisecond RF pulse characteristics. Presently, no other approach exists that provides command OFF ability and high current and large pulse width capabilities when driven by a single high voltage power supply.
The first advantage of the present invention over the prior art approach is that the high voltage power supply does not need to be turned off in order to extinguish each magnetron pulse. The IGBT devices are ON/OFF controllable devices.
The second advantage of the present invention is that IGBT devices require minimal drive power to operate on the order of milliwatts, whereas the prior art approach requires hundreds of watts which produces excess heat. The low power consumption here will allow a much smaller and lighter high voltage isolation transformer to be used.
The third advantage of the present invention is that the IGBT devices can be switched on prior to the high voltage power supply, which offers a smoother voltage rise time on the magnetron instead of the voltage pedestal effect normally encountered when the magnetron goes from low to high level oscillation. The low level oscillation refers to a level at which the magnetron draws a minimal amount of current but maintains itself in a conduction mode. This allows the magnetron to be less sensitive to the pedestal voltage rise time used to place the magnetron at its full power operation. Also, by switching prior to the high voltage pulse, the switching losses in the IGBT device are greatly reduced.
The present invention may be advantageously used with one or more magnetron devices having high PRF. The principles of the present invention may be used in instances where magnetrons must have small size and weight.
The solid state magnetron switcher of the present invention offers command OFF capability, requires only milliwatts of drive power, and is very efficient. Furthermore, the solid state magnetron switcher of the present invention is also smaller and lighter than the prior art devices.
A key aspect of the present invention is to place each magnetron into low level oscillation by using the correct value of resistance between the high voltage power supply and the magnetrons. This minimizes the voltage across each IGBT device.
The IGBT switches can be switched between magnetrons at a maximum rate of several KHz (i.e., 10-20 KHz) limited by pulse width, number of magnetrons, average power available, and switching speed of the IGBT devices. Interpulse switching times between array elements primarily depend on the limitations of the high voltage power supply. The technological approach of the present invention offers fast ON and OFF pulse commands with large pulse widths (i.e., microsecondsxe2x80x94seconds) typically around several milliseconds.